PURPOSE: To obtain a motion signal exactly showing the handwriting of a pen point, to reduce the data quantity corresponding to the character of the motion signal and to embody a small-sized and highly accurate acceleration detector.

CONSTITUTION: Plural motion detection means 103 and 104 are provided at the different distances from a pen point, and the motion signal at the pen point location is obtained based on the motion signal from these detection means. Handwriting information is composed of the time-series coordinate data corresponding to each point on a moving locus. Based on a plurality of coordinate data in the past, the location of the next coordinate data is predicted. Based on a predicted error, the next coordinate data is properly abolished. Within the two coils provided so that the coils may integrally move in only a prescribed direction when the external force by acceleration is added, the induced voltage according to the acceleratior is made to be outputted from the first coil, the driving current according to this induced voltage is formed, the current is imparted to a second coil, and the force in the opposite direction which is equal to the moving force for the first coil is made to be generated in the second coil. The voltage proportional to the driving current is defined as an acceleration signal.